The present invention relates to an electrophotographic image forming apparatus for use in a copying machine, a printer, a facsimile and other machines and more particularly to a method for driving an image carrier and a transfer member of the image forming apparatus.
Hitherto, an image is formed by an electrophotographic image forming apparatus by forming a latent image on an image carrier by using latent image forming means and by transferring the image developed by developing means to a transfer member. However, such image forming apparatus has had a problem that the image may be expanded/contracted due to nonuniformity of speed of the image carrier.
In order to deal with such a problem, there have been proposed various methods for suppressing the nonuniformity of speed of the image carrier. Japanese Patent Application Laid-Open No. Hei. 4-204859 has proposed a method of suppressing the nonuniformity of speed of the image carrier by detecting a peripheral speed of the image carrier and by modulating a driving speed of a driving source corresponding to the detected peripheral speed.
Japanese Patent Application Laid-Open Nos. 62-264067 and 63-11965 have also proposed methods of suppressing the expansion/contraction of the image by arranging so that a time during which the image carrier moves from a position where a latent image is formed thereon by latent image forming means to a position where the image on the image carrier is transferred to a transfer member is integer times of a cycle of nonuniformity of speed of a driving source or an image carrier driving member to cancel the nonuniformity of speed of the driving source and the image carrier driving member in writing the latent image and transferring the image.
However, the method proposed in Japanese Patent Application Laid-Open No. Hei. 4-204859 described above has had a problem that it requires a high precision speed detector for detecting the peripheral speed of the delicate image carrier and an expensive feedback circuit for controlling the driving source based on the detected result and that a low inertial image carrier has to be realized in order to realize quickly response in controlling the speed, increasing the cost of the image forming apparatus.
Further, the methods proposed in Japanese Patent Application Laid-Open Nos. 62-264067 and 63-11965 have had a problem that although the nonuniformity of speed of the driving source for driving the image carrier and the drive transmitting means may be canceled, the nonuniformity of speed caused by eccentricity and geometrical error of the image carrier driving member which operates along with the image carrier such as a gear attached to the image carrier cannot be canceled. They also have had a problem that because the nonuniformity of speed of the image carrier is directly influenced by the nonuniformity of speed caused by the image carrier driving member which operates along with the image carrier, the image carrier driving member which operates along with the image carrier has to be mounted with extremely high precision or has to have an extremely high precision profile.
Further, when the image forming apparatus is equipped with a plurality of developing means to form a color image by transferring an image on the image carrier to a transfer member by laying one after another, the nonuniformity of speed of the image carrier affects the image quality not only as the expanded/contracted image but also as displacement in color or nonuniformity of color. When the nonuniformity of speed is the same, people have a much higher visual sensitivity to the displacement in color or the nonuniformity of color than that to the expansion/contraction of an image in general. Therefore, the image carrier used in the image forming apparatus for forming color images is required to be driven with extremely high precision.
In order to prevent the speed variation caused by the backlash between the driving gears, there has been one disclosed in Japanese Patent Application Laid-Open No. Hei. 5-289536 for example. The publication No. Hei. 5-289536 discloses a mechanism arranged such that drive is transmitted from a gear for driving an intermediate transfer belt to a gear for driving a photoreceptor belt and a peripheral speed of the photoreceptor belt is slightly faster than that of the intermediate transfer belt. It is intended to transmit driving force stably by arranging so that the gear for driving the photoreceptor belt engages with the gear for driving the intermediate transfer belt always in a certain direction by causing frictional force produced between the photoreceptor belt and the intermediate transfer belt to act as a load.
Further, in the publication described above, a driving roller for driving the intermediate transfer belt is disposed, with respect to the direction in which the intermediate transfer belt is conveyed, on the upstream side of a primary transfer position where a toner image on the photoreceptor belt is transferred to the intermediate transfer belt, and the intermediate transfer belt is wound in circular arc around the photoreceptor at the primary transfer position.
In the arrangement described above, however, the frictional force at the primary transfer position is not stable due to the variation of quantity of toner adhering on the photoreceptor belt and the intermediate transfer belt and to the variation of surface potential of the photoreceptor belt and the intermediate transfer belt. Still more, because the primary transfer position is located on the side where the intermediate transfer belt is pushed out from its driving roller (on the so-called loose side), there has been a problem that not only the speed of the intermediate transfer belt but also an angle of abutment of the intermediate transfer belt before and after the primary transfer position vary due to the variation of the frictional force at the primary transfer position, causing deterioration of image such as dispersion of the toner image during the primary transfer.
Further, the above-mentioned arrangement has had a problem that when the frictional force at the primary transfer position varies to a large extent, the intermediate transfer belt is loosened and the intermediate transfer belt vibrates, thus disturbing the image.
The above mentioned arrangement has had also another problem that when the friction force at the primary transfer position is not enough, the speed variation occurs due to the backlash of the driving gears, thus causing the displacement and nonuniformity of colors in the end.
The image forming apparatus using the electrophotography has had a problem that its structure is complicated, its size is large and it is difficult to maintain.
Then, in order to improve the maintenance of the equipment, Japanese Patent Application Laid-Open Nos. Hei. 3-249765 and Hei. 7-199768 have been proposed for example as an image forming apparatus arranged so that consumable can be readily replenished or replaced.
Japanese Patent Application Laid-Open No. Hei. 3-249765 has disclosed an arrangement in which an image carrier and a plurality of developing means are unitized into a body in a manner capable of being attached/removed.
However, being different from the image forming apparatus for forming a monochromatic image (only black for example), the image forming apparatus for forming a multi-color image has a plurality of developing means and its image carrier is relatively large, so that when they are unitized into a body, the unit turns out to be a considerably large and heavy unit. It is then practically very difficult to replace such unit in the image forming apparatus for forming multi-color images.
Still more, because consumption of each toner of the plurality of developing means is different, it is wasteful to unitize them because other developing means also cannot but be replaced when toner of any one of the developing means is all consumed.
Then, it is necessary to allow the image carrier, the developing means and the like to be replaced separately.
Further, a so-called laser scan optical system and the like comprising a step of scanning the image carrier by laser light is generally used as the latent image forming means and it is very sensitive to vibrations and shocks, so that when a dislocation occurs in the optical parts composing the laser scan optical system, it turns out to be a shear in colors in the image forming apparatus for forming a multi-color image even if it is a minor dislocation which poses no problem in the image forming apparatus for forming a monochromatic image. Then, it is necessary to be able to replace the image carrier, the developing means and others without moving the latent image forming means.
Further, while there may be a case when the latent image forming means receives a shock when the image carrier, the developing means or the like drop on the equipment proper by accident in replacing them, it is necessary to dispose the latent image forming means such that the locus of the image carrier, the developing means and others in attaching/removing them will not pass above the latent image forming means so that the shock is minimized.
Japanese Patent Application Laid-Open No. Hei. 7-199768 has disclosed an arrangement in which the image carrier, the developing means and others are attached/removed, respectively, in the direction of the axis of the image carrier.
However, because the image carrier, the developing means and others have a lengthy shape in the direction of the axis of the image carrier, it is difficult to insert one end thereof to an attaching/removing opening while holding only the other end. Because a driving section or an electrode section of the image carrier and the developing means is disposed on the opposite side from the side held in attaching/removing the image carrier and the developing means and it becomes the head in inserting to the equipment proper, there may be a case when the new image carrier or developing means becomes unusable when it is hit with the attaching/removing opening and is damaged in inserting thereto.
Further, while A4 size recording sheets had been the main stream in the image forming apparatus for forming a monochromatic image, it has come to be required to be able to accommodate with recording sheets larger than the A4 size, e.g. A3 or more, for the image forming apparatus for forming a multi-color image due to the increase of demand in the multi-color printing lately. Due to that, because the image carrier, the developing means and the like would have a shape which is even longer in the axial direction of the image carrier in the image forming apparatus which accommodates with the recording sheet larger than the A4 size in particular, it becomes more difficult to attach/remove them in the axial direction of the image carrier.
Still more, as means for helping the attachment/removal of the image carrier, the developing means and the like having the lengthy shape in the axial direction of the image carrier into/from the equipment proper, there have been proposed an arrangement in which guide grooves for moving the image carrier, the developing means or the like in the axial direction or a movable table for carrying and moving the image carrier, the developing means or the like are provided on the side of the equipment proper or an arrangement in which such auxiliary means is allowed to be drawn out. However, because a distance in moving the image carrier, the developing means and the like from the attaching/removing opening to the attachment position within the equipment proper becomes longer in attaching/removing in the axial direction than that of the case in attaching/removing in the direction vertical to the axial direction, it becomes difficult to attach/remove them when the linearity of the guide groove is not enough. Further, because the guide groove is long, it tends to be clogged by some objects, making it difficult to attach/remove them in the end.
Further, because one end of the image carrier, the developing means or the like having the lengthy shape in the axial direction of the image carrier is inserted to the attaching/removing opening of the equipment proper while holding the other end thereof in attaching/removing them to/from the equipment proper in the axial direction, the image carrier, the developing means or the like which is cantilevered tends to deflect or distort.
In particular, because the developing means used in the image forming apparatus for forming a multi-color image is repeatedly contacted/separated with/from the image carrier within the equipment proper, it tends to deflect or distort, disallowing good images to be obtained stably, when it is arranged such that when it is moved by supporting only the side face or the both ends thereof or by abutting it with a movable member such as a roller under the developing means when it is mounted within the equipment proper.
Therefore, although it is necessary to give enough strength to the image carrier, the developing means and the like so that they will not deflect in the axial direction, it becomes a factor of increasing the cost of those replaceable members.
Further, because the image carrier and the like are attached/removed in the direction vertical to the sheet conveying direction in the arrangement in which the image carrier, the developing means and the like having the lengthy shape in the axial direction of the image carrier are attached/removed to/from the equipment proper in the axial direction, a jammed paper may damage the image carrier and the like or the paper may be torn, damaging the whole equipment as its piece moves within the equipment proper (back at the opposite side from the attachment/removal port where it is hard to reach) if one tries to attach/remove the image carrier, the developing means or the like by mistake in the state when the paper is jammed within the main body. Further, such arrangement requires means for removing a paper jammed within the equipment proper, beside the opening for attaching/removing the image carrier, the developing means or the like.
Further image forming apparatus, there have been known ones disclosed in Japanese Patent Application Laid-Open No. Hei. 1-134475 and in Japanese Patent Application Laid-Open No. 61-95370 for example. The former image forming apparatus comprises an electrostatic latent image carrier, a plurality of developing units disposed adjacent to and around the electrostatic latent image carrier, and developing unit separating/contacting means comprising horizontal separating/contacting means for horizontally moving the developing unit and turning separating/contacting means for turning the developing unit. The latter image forming apparatus holds a plurality of developing units in a shape of Ferris wheel and has a development unit composed of a movable supporter capable of moving a required developing unit along a predetermined path to one developing position common to respective color developing units.
The latter is also provided with position detecting means for detecting a stop position for stopping the developing unit held like Ferris wheel at a certain position.
In the example disclosed in Japanese Patent Application Laid-Open No. Hei. 1-134475 described above, however, the means for separating/contacting the plurality of developing units comprises the horizontal separating/contacting means for horizontally moving the developing unit and the turning separating/contacting means for turning the developing unit, so that there mixedly exited two kinds of developing unit moving means for moving the developing unit to the developing position where the developing unit is approached to the electrostatic latent image carrier or the standby position where the developing unit is separated from the electrostatic latent image carrier, thus complicating the equipment. Further, the example disclosed in Japanese Patent Application Laid-Open No. 61-95370 has had a problem that the equipment is complicated because the plurality of developing units are held and unitized like the Ferris wheel and hence, a number of elements composing the developing units and the developing unit moving means increases. Still more, it has been difficult to miniaturize it because the size of the components has been apt to increase to hold and unitize the developing units like the Ferris wheel. Further, because a distance for moving the developing unit to the developing position where it is approached to the electrostatic latent image carrier or the standby position where it is separated from the electrostatic latent image carrier is prolonged, it took a long time to move the developing unit and it has been difficult to provide an image forming apparatus capable of outputting images at high speed.
Further, the example disclosed in Japanese Patent Application Laid-Open No. 61-95370 has had a problem that the equipment is complicated because it has been provided with the position detecting means such as a photosensor in order to detect the stop position of the developing units held like the Ferris wheel and it required numbers of elements composing the equipment.
Accordingly, the present invention has been devised in view of such problems and is intended to provide an inexpensive image forming apparatus which is capable of forming high quality images by canceling the nonuniformity of speed to suppress the expansion/contraction of the image even if there is the nonuniformity of speed caused by the image carrier driving member which operates along with the image carrier.
The present invention is also intended to provide an image forming apparatus, when applied thereto which is equipped with a plurality of developing means and in which images on the image carrier is transferred to a transfer member one after another, which is capable of forming high quality images by correcting the displacement in color or nonuniformity of color caused by the nonuniformity of speed of the image carrier with high precision.
It is another object of the present invention to solve the aforementioned problems by providing an image forming apparatus which is capable of driving the photoreceptor in synchronism with the intermediate transfer belt with a simple arrangement and, hence, of providing images finely reproduced.
It is a further object of the invention to solve the aforementioned problems that the image carrier, the developing means or the equipment proper is apt to be damaged if the image carrier or the developing means having the lengthy shape in the axial direction of the image carrier is attached/removed in the axial direction and that the latent image forming means is apt to be damaged in attaching/removing the image carrier, the developing means or recording member storage means.
It is a further object of the invention to solve the aforementioned problems that the image carrier or the equipment proper is apt to be damaged when the image carrier and the like is attached/removed in the state when a recording member is jammed within the equipment proper, that an equipment opening section has to be provided beside the opening for attaching/removing opening the image carrier, the developing means and the like and that an installation area of the equipment proper is large.
It is a further other object of the invention to solve the aforementioned problems that the developing means having the lengthy shape in the axial direction of the image carrier is apt to deflect and that no good image cannot be formed if it deflects when it is attached to the equipment proper.
It is a further object of the invention to solve the aforementioned problem that the installation area of the equipment is large.
It is a further object of the invention is to provide an image forming apparatus having a simple structure with less power source by arranging so as to have selective driving means for selectively driving first developing unit or second developing unit selected among a plurality of developing units by driving the driving motor forward or backward and also so as to have selective driving means for selectively driving first developing unit moving means or second developing unit moving means selected among a plurality of developing unit moving means by driving the driving motor forward or backward.
Further, the present invention is intended to provide an image forming apparatus which takes less time to move the developing unit and which is capable of outputting images at high speed by composing the developing unit moving means, for moving the developing unit to the developing position where it is approached to the latent image carrier or the standby position where it is separated from the latent image carrier, by supporting means for rockably supporting the developing unit; urging means for rocking and urging the developing unit in one direction; and a cam mechanism for rocking and moving the developing unit in the other direction.
Further, it is intended to provide a rotation transmitting unit which requires no position detecting member for detecting the rotation stop position of a rotation output shaft.
It is also intended to provide an image forming apparatus, which requires no position detecting means for detecting the developing position or the standby position of the developing unit, which is inexpensive and which has a simple structure, by arranging such that the rotation transmitting unit is used, one turn of the transmitting means of the rotation transmitting unit is divided into half, and turning force is transmitted from an input shaft to an output shaft sequentially by each partial angle by inputting pulses from control means.